What is the harmonic minor scale?
Definition
Harmonic minor is the natural minor scale with the 7th note raised a half step. Formula: 1 2 b3 4 5 b6 7. In E: E F# G A B C D#.
Why it sounds the way it does
That raised 7th sits just a half step below the root, so it pulls hard back home. It's the tense, classical sound behind neoclassical shred and a lot of melodic death metal and power metal. The gap between the b6 and the raised 7th (C to D# in E) is what gives it its exotic edge.
See it in tab, next to the other metal scales: metal scales for guitar.